I think you need to lock him up now or he goes to free agency. Any discount you get in a Crochet extension ticks away with each passing day. By the time you get to next offseason, you have a Corbin Burnes situation where he's just going to let it ride to free agency.
Given Crochet's injury history and lack of starting experience, he *should* be willing to sacrifice a few years of FA for a payday today. It's risk mitigation for a pitcher in today's game. A year from now, that's less likely.